Broadband Internet network infrastructure is developing at rates that exceed the most aggressive analyst predictions. In the consumer market sector, telecommunications, cable and wireless companies have accelerated deployment of broadband capability to the home with xDSL, cable modem or wireless last mile rollouts. In the corporate market sector, broadband infrastructure is already available for desktop computing applications.
Broadband provides a foundation for the use of good quality IP video in Internet applications. Traditionally limited to Intranets or private networks, broadband Internet connectivity is paving the way for video-based applications such as Internet advertising with video, rich media on web pages, video-assisted e-commerce (video catalogs, travel, etc.), event webcasting, personalized information on demand (news, sports, medicine, lectures, movies, etc.), personal video exchanges, and training and corporate communications.
Compared to the low frame-rate, small sized videos traditionally found on the Internet and delivered on narrowband connections, advances in compression technologies have made reasonable quality video possible at connection rates of 300 Kbits/sec (Kbps) or higher. News stories and lectures with very little motion or action can be sent at lower bit rates of approximately 100 Kbps to 200 Kbps. Video with a lot of movement, like a fashion show, needs a higher bit rate to capture the motion and detail of the scene. For a content provider considering Internet distribution, 300 Kbps could be considered acceptable, and 1 to 1.5 Mbps, excellent. Video catalogues, advertisements, and other commerce-related uses of video require that the product be presented at the highest quality levels possible. Broadband rates of 1.5 Mbps and higher afford 30 frames per second (fps) video with CD quality audio. Content with a lot of movement, such as auto racing, needs even higher bit rate, as high as 3 to 4 Mbps.
As Broadband connections proliferate, demand for better performance has fostered an industry focused on speeding up the delivery of Internet content. The majority of these solutions have centered on smaller objects such as text and images. Due to its sheer size, video is one of the most difficult data types to manage on the Internet. A five-minute video clip, encoded and compressed at 1.5 Mbs is 56 Megabytes in size. Video also has strict timing requirements. A frame arriving past its presentation time ({fraction (1/30)} sec in the case of a 30 fps video) is useless and the user experiences jerky playback. Given these stringent requirements, delivering quality video over broadband is a challenging problem.
While deployment of the broadband infrastructure is an important step in enabling streaming video over the Internet, upgrades to connectivity and bandwidth alone do not assure the delivery of quality video to large audiences with minimal start-up latencies. When video is streamed to the end user via the Internet backbone, video quality is often impacted by problems. When the source of the video is not close enough to the end user, packet losses can severely compromise video quality. Packet losses result from congestion buffering introduced by network switches and routers between the video source and the end user. Current bandwidth costs (satellite and terrestrial) make it impractical to stream high-quality video from a server to the end user on a point-to-point basis.
Existing solutions geared towards improving the performance of accessing web pages containing rich media (typically images) are increasingly being used to address the problems with streaming video on the Internet. Currently, there are two classes of solutions that have been employed for improving performance on the Internet: content delivery networks and caching solutions.
Content Delivery Networks
Most content delivery networks employ architecture commonly referred to as distributed content services (DCS). Under DCS, portions of web pages containing large amounts of content such as images are replicated (“pushed”) on a number of edge servers deployed in last-mile service provider locations close to the edges of the network, as shown in FIG. 1. When a user accesses such a web page, the edge server closer to the user is directed to serve the replicated content to the user. This solution avoids moving large files through the network backbone for frequently used content. Avoiding the backbone can improve performance (since there are fewer hops between a strategically placed edge server and the client) and is a more cost-effective and scalable solution. Content delivery networks generally use private satellite and terrestrial networks to connect the originating server to the edge servers. This solution has been widely deployed to improve the delivery of small media types such as static images and streaming audio on web pages.
Caching Solutions
In the caching solutions approaches, when a user first accesses a web page containing static content (images, audio, video), content is served directly (“pushed”) from the origin server and is subsequently cached by a caching server. Caching servers are placed at strategic points in a network (typically an ISP network) that are closer to the end users. On subsequent access of the same pages, the cached content is served directly to the end user (FIG. 2). Caching systems consist of specialized equipment at the service provider locations that monitor URL requests for web objects. Serving content from cached server can reduce Internet backbone traffic up to 50% thus reducing bandwidth costs. Serving content from a cache closer to the end user also improves performance for the reasons outlined in the first approach.
The current methods for content delivery and caching are not optimal for the delivery of high-quality video. Current content delivery networks ensure guaranteed response times by storing all of the response-time sensitive data at the edges of the network. Users ensure response times by paying for storage costs. The main assumption here is that storage costs are significantly lower than bandwidth costs associated with transporting data over the backbone. The sheer sizes of high-quality, full-frame rate video on broadband networks require a reexamination of the storage vs. bandwidth issue. To illustrate this issue, consider emerging applications of broadband video on the Internet:
Delivery of Personalized Information on Demand
Customized delivery of information rich in video content (new, sports, entertainment, personal health etc.) is a growing application segment on the broadband Internet. A five-minute video segment at 1.0 Mbps amounts to 37.5 megabytes. One such channel of video, which is a 24-hour segment split into 5 minute segments amount to about 10 gigabytes of storage. A hundred such channels amount to 1 terabyte. Such media stored on 1000 edge servers amount to 1 petabyte of storage for one day's worth of video.
Content Delivery Network Approach Issues
From hardware cost perspective, it is impractical to store all of the data inside the edge networks. Additionally, floor space is at a premium at central offices and cable head-ends where the servers and storage need to be deployed. An intelligent placement of data based on measured and anticipated usage is certainly more practical. Storage issues involve more than just disk space. An 18-gigabyte disk may be large enough to hold approximately two days of one channel at an edge server. However, at current disk bandwidth rates (approximately 50 Mbps), a disk may have capacity to serve 50 users simultaneously. To serve more users, the data need to be replicated appropriately, adding to the storage costs significantly.
Caching Approach Issues
Networks that use pure caching solutions also suffer from problems due to the sheer size of the objects they are required to cache. If a media object is not found in the cache, it takes a certain amount of time before the requested media object is found and the cache is loaded. To most users, this latency is unacceptable. Once cached, the system behaves as a content delivery system described above. However, for any reasonable size cache, the number of objects that can be cached is fairly small leading to high rate of cache misses.
Thus, an optimal solution for streaming video over the Internet is greatly needed. The current popular solutions have been designed for delivering static images and streaming audio over the Internet and are unable to meet streaming video requirements.